Aluminum conductor paste for back surface passivated cells with locally opened vias

Abstract

This invention relates an aluminum conductor paste formulation and its method of application on rear side passivated locally opened vias; dot or line geometry or combination thereof employing laser ablation or chemical etching methods. Such Back Surface Passivated Si-solar cells include dielectric layers of Al203, SiNx, Si02, SiC, α-Si, Si02/SiNx, Al203/SiNx, Si02/Al203/SiNx. The Al-conductor paste of this invention achieves; (i) non-degradation of passivation stack, (ii) defect free surfaces and void free vias, (iii) a strong and uniform Back Surface Field (BSF) layer within dot vias and line vias.

1 . A paste composition comprising, prior to firing:
 a conductive metal component comprising aluminum;   a glass component;   a vehicle; and   at least one organometallic compound including an element selected from boron, silicon, vanadium, antimony, phosphorous, yttrium, titanium, nickel, cobalt, zirconium, zinc, lithium and combinations thereof.   
     
     
         2 . (canceled) 
     
     
         3 . The paste composition of  claim 1 , wherein the organometallic compound includes at least one C 1 -C 50  organic moiety that is linear or branched, saturated or unsaturated, aliphatic, alicyclic, aromatic, araliphatic, halogenated or otherwise substituted, optionally having one or more heteroatoms such as O, N, S, or Si, and/or including hydrocarbon moieties such as alkyl, alkyloxy, alkoxide, alkylthio, or alkylsilyl moieties. 
     
     
         4 . The paste composition of  claim 1 , wherein the organometallic compounds are selected from the group consisting of metal ethoxides, metal acetonates, metal acetylacetonates, metal carboxylates, metal 2-methylhexanoates, metal 2-ethylhexanoates, and metal 2-propylhexanoates, metal acrylates, metal methacrylates, and combinations thereof, wherein the metal is selected from the group consisting of titanium, zirconium, nickel, cobalt, zinc, vanadium, and combinations thereof. 
     
     
         5 . (canceled) 
     
     
         6 . The paste composition of  claim 1 , further comprising an Al—Si alloy, an Al—Si eutectic alloy, or both. 
     
     
         7 . (canceled) 
     
     
         8 . The paste composition of  claim 1 , wherein the conductive metal component further comprises up to 20 wt % of at least one of an Al—Si eutectic, zinc, tin, antimony, silicon, bismuth, indium, molybdenum, palladium, silver, platinum, gold, titanium, vanadium, nickel, copper, and combinations thereof, based upon 100% total weight of the paste composition. 
     
     
         9 . The paste composition of  claim 1 , wherein the glass component includes at least one selected from the group consisting of (a) Bi—Zn based glasses, (b) borosilica glasses, (c) alkali-titanate glasses, (d) lead-glasses, and combinations thereof. 
     
     
         10 . The paste composition of  claim 1 , wherein
 the conductive metal component comprises about 40 to about 80 wt % of an aluminum source,   the glass component is present to an extent of about 0.1 to about 10 wt %, and   the vehicle is present to an extent of about 5 to about 30 wt %, all based upon 100% total weight of the paste composition.   
     
     
         11 . The paste composition of  claim 10 , further comprising about 0.1 to about 10 wt % of an organic or inorganic additive compound. 
     
     
         12 . The paste composition of  claim 1 , wherein the glass component comprises two or more glasses. 
     
     
         13 . The paste composition of  claim 1 , wherein the D 50  particle size of the glass component is about 0.1 microns to about 20 microns. 
     
     
         14 . The paste composition of  claim 5 , wherein the aluminum is provided in powder form having a bimodal particle size distribution, wherein a first D 50  average aluminum particle size is in the range of 0.5 to 3 microns and a second D 50  average aluminum particle size is 3-40 micron range, wherein no overlap is intended. 
     
     
         15 . (canceled) 
     
     
         16 . The paste composition of  claim 1 , wherein the viscosity of the paste is in the range of 5-80 Pa·s. 
     
     
         17 . The paste composition of  claim 1 , wherein the metal component comprises both flake and spherical morphologies. 
     
     
         18 . The paste composition of  claim 1 , wherein organic vehicle includes oleic acid, Duomeen TDO (tallowpropylene diamine dioleate) and DisperBYK® 111 (a copolymer with acidic groups having an acid value of 129 mg KOH/g, a density of 1.16 and a flash point over 100° C.). 
     
     
         19 - 31 . (canceled) 
     
     
         32 . A photovoltaic cell comprising a silicon wafer and a back contact thereon, the back contact comprising a passivation layer opened locally at least partially coated with a fired back side paste, the back side paste comprising, prior to firing:
 a conductive metal component comprising aluminum;   a glass component;   a vehicle; and   at least one organometallic compound including an element selected from boron, silicon, vanadium, antimony, phosphorous, yttrium, titanium, nickel, cobalt, zirconium, zinc, lithium and combinations thereof.   
     
     
         33 - 39 . (canceled) 
     
     
         40 . A method of making a photovoltaic cell contact, comprising:
 a. applying a paste composition to a locally opened rear passivation layer on a silicon substrate, the paste comprising a conductive metal component comprising aluminum, a glass component, a vehicle, and at least one of an organometallic additive compound, phosphate glass and phosphorus compound dispersed in the vehicle, wherein the organometallic compound is selected from boron, silicon, vanadium, antimony, phosphorous, yttrium, titanium, nickel, cobalt, zirconium, zinc, lithium and combinations thereof, wherein the organometallic compound can include C 1 -C 50  organic moieties that are linear or branched, saturated or unsaturated, aliphatic, alicyclic, aromatic, araliphatic, halogenated or otherwise substituted, optionally having one or more heteroatoms such as O, N, S, or Si, and/or including hydrocarbon moieties such as alkyl, alkyloxy, alkoxide, alkylthio, or alkylsilyl moieties; and   b. heating the paste to sinter the conductive metal component.   
     
     
         41 - 43 . (canceled) 
     
     
         44 . The method of  claim 40 , wherein the passivation layer comprises at least one selected from the group consisting of SiNx, Al 2 O 3 , SiO 2 , SiC, amorphous Si, TiO 2 , Al 2 O 3 /SiNx, SiO 2 /SiNx, SiO 2 /Al 2 O 3 /SiNx in a combined thickness of about 5 to about 360 nm thick. 
     
     
         45 . The method of  claim 40 , wherein the local openings are made by laser ablation or chemical etching using an etchant comprising phosphorus, to form dots or lines, wherein the dot diameter ranges from 20-200 microns and a trench is 100-700 microns wide, or the dot diameter ranges from 20-200 microns and a trench is 0.5-2.0 mm wide. 
     
     
         46 - 48 . (canceled)